The invention generally relates to circuitry for damping or averaging signal fluctuations driving a fuel gauge. More specifically, the invention concerns a damping circuit to be placed between the variable resistance output of a fuel tank sending circuit and the driving input to a fuel gauge.
False fuel gauge indications in vehicles such as automobiles are often generated as a result of the vehicle's acceleration, going uphill or downhill, cornering or undergoing any other operation that causes the fuel to "slosh" about or otherwise vary in a highly transient manner. Known approaches to dealing with the "sloshing"problem appear to involve relatively complex arrangements such as utilization of microcomputers for averaging the analog level readings obtained from the tank sender circuit. Related known patents in this area are the following U.S. Pat. Nos.: 4,402,048; 4,497,205; 4,470,296; 4,250,750; 3,938,117; 3,727,182; 3,649,911; 3,638,115; and 2,356,617.
U.S. Pat. No. 4,402,048--Tsuchida et al discloses a microcomputer-based system for indicating fuel quantity wherein the limit values about a center reading are used to discriminate against abnormal sudden changes caused by sloshing.
U.S. Pat. No. 4,497,205--Zulauf et al discloses a liquid level sensor using a variable flux generating coil to indicate the level. The monitoring circuit includes a filter means which reduces the response of the circuit to transient indications caused by sloshing.
U.S. Pat. No. 4,470,296--Kobayashi et al discloses a fuel gauge wherein the fuel level signal is averaged over time intervals which vary according to whether the fuel level is "stable" or "unstable". When the fuel level is deemed unstable the averaging time interval is selected to be longer than that used when the fuel level is stable. Stability is determined by a variety of vehicle sensors, such as speed sensors.
U.S. Pat. No. 4,250,750--Martinec et al discloses a liquid level measuring system wherein a microprocessor drives a bar graph type display. The microprocessor program compares each sample to a last sample and does not alter the bar graph display output unless several consecutive samples indicate a need to alter the displayed gauge indication.
U.S. Pat. No. 3,727,182--Snyder teaches a dual sensor monitoring and signal warning circuit for indicating a low brake fluid level in either reservoir of a split master brake cylinder. A resistive-capacitive time delay prevents energization of a warning lamp to prevent flickering in the event of brake fluid sloshing.
U.S. Pat. No. 3,398,117--Bozoian, similar to the '182--Snyder Patent, concerns a critical liquid level warning circuit with delay interposed to prevent a false low fuel warning in the event of fuel sloshing.
U.S. Pat. No. 3,649,911--Swanson teaches a meter driver circuit for improving meter responsiveness. The invention is directed principally to a circuit for initially overdriving a meter to overcome friction and inertia of the meter movement.
U.S. Pat. No. 3,638,115--Grundy discloses a meter jitter minimizing circuit.
U.S. Pat. No. 2,356,617--Rich discloses circuitry for providing sudden capacitive current in-rush to speed the response of a meter movement.
There is a need for a relatively simple and economical circuit for damping undesirable variations in input signals from a fuel tank sending unit prior to sending the filtered indicator signals to a utilization device such as an air core magnetic fuel indicating gauge.